请问GWD-6-Q1中while doing sth的用法

The themes that Rita Dove explores in her poetry is universal, encompassing much of the human condition while occasionally she deals with racial issues.

A.        is universal, encompassing much of the human condition while occasionally she deals

B.        is universal, encompassing much of the human condition, also occasionally it deals

C.       are universal, they encompass much of the human condition and occasionally deals

D.       are universal, encompassing much of the human condition while occasionally dealing

E.        are universal, they encompass much of the human condition, also occasionally are dealing

答案是D，这个我能推出来，根据主语复数，和run-on sentence很容易推出D，但是我想问下

在前人给出的D的解释中：『while doing sth是做时间状语，当主语重复时被省略，且助动词一并省略；』这句话我不是很明白，而且while在这里的意思我也不太明白，谢谢！

在前人给出的D的解释中：『while doing sth是做时间状语，当主语重复时被省略，且助动词一并省略；』这句话我不是很明白，而且while在这里的意思我也不太明白，谢谢！